Breast prostheses are used on a large scale after surgical removal of mammary carcinomas. They are usually made of a plastic composition, especially a synthetic silicone resin that cures to a gelatinous state, and the outer surface of the prosthesis is modeled to simulate the shape of the breast. Breast prostheses can be designed as either solid or hollow prostheses, but in the latter case the side of the prosthesis facing the body is hollowed out and has a concave configuration.
A distinction is made between film-free breast prostheses and prostheses sheathed in film. Film-free breast prostheses, which constitute only a small percentage of the prostheses currently on the market, have the disadvantage that they are tacky to the touch because the silicone resin composition often does not crosslink completely and uncrosslinked silicone oil seeps out.
In order to overcome this disadvantage, breast prostheses are sheathed with thermoplastic films, especially polyurethane films In general, such breast prostheses are produced by placing the uncrosslinked silicone resin composition together with the crosslinking agent and a catalyst between two flat films that form an envelope for the prosthesis. The films are welded together along this edge except for a small filling opening The films are then fixed at the edge of a cavity in the area of the welded edge in a die that corresponds to the shape of the breast. Silicone resin composition is added until the films are pressed against the walls of the die cavity, the film edges are then welded together in the area of the filling opening, and the silicone resin composition in the die at that point is crosslinked at an elevated temperature so it cures to form a gelatinous mass.
Breast prostheses of this type are described, for example, in German Patent Publications 2,701,627, 2,737,321 and 2,902,373.
However, welding the film edges together, especially in the area of the filling opening, poses problems when residues of the injected silicone resin composition are between the films. These residues prevent satisfactory welding of the film edges so the weld seam easily tears open and the silicone resin composition easily escapes during the curing process as well as after curing when even a slight pressure is applied to the prosthesis. Furthermore, the dies must be heated to a relatively high temperature (about 130.degree. C.) in the welding and crosslinking operation and must be cooled between each step, which is very time consuming and expensive.
Another disadvantage of the welding process is that the welding electrodes applied to both films must fit precisely in order to produce a stable weld. This is practically possible only if the contacting surfaces are exactly flat. A breast prosthesis produced in this way is therefore flat on the side facing the body, so that undesirable folds develop when the prosthesis is positioned on the body.
Furthermore, known breast prostheses have only a low dimensional stability because of their natural softness and they can deform under their own weight if the dimensions of the prosthesis do not conform exactly to the dimensions of the brassiere.
In order to overcome these disadvantages, German Patent 3,336,279 proposes a breast prosthesis that consists of a synthetic resin composition cured to a gelatinous consistency and enclosed between two thermoplastic films welded together and composed of two layers of different strengths. This breast prosthesis is characterized in that the layer facing the human body has a higher strength and consists of condensation-crosslinked silicone resin. On top of this layer is a layer that faces away from the human body, has a lesser strength and is made of an addition-crosslinked silicone resin. The insides of the thermoplastic films have a layer of an adhesion promoter that is effective with respect to the condensation-crosslinked silicone resin at least in the areas of the edges.
According to the improvement for this prosthesis described in German Patent Application 3,416,240, the crosslinking temperature should be in the lower part of the plastic range of the film.
In producing this breast prosthesis, it is not necessary to leave an opening for injecting the curable synthetic resin composition. However, use of an adhesion promoting layer is necessary because the quantity of synthetic resin for producing the layer that faces the body cannot be metered precisely and yet it must be measured in such a way that the synthetic resin composition necessarily come to lie between the outer edge areas of the films. Furthermore, development of folds is often observed when producing such prostheses.